Recently, as electronic apparatuses have been miniaturized, demands for high-capacity secondary batteries have been increased. In particular, lithium ion secondary batteries, which have a higher energy density and better large-current charge/discharge characteristics than those of nickel-cadmium batteries and nickel-hydrogen batteries, are attracting attention. Although studies to increase the capacity of a lithium ion secondary battery have been conventionally widely carried out, it has been required that a lithium ion secondary battery has further improved capacity, large-current charge/discharge characteristics, high-temperature preservation property and high cycle characteristics, due to the increasing demand for a lithium ion secondary battery having a better performance.
A graphite material and amorphous carbon are often used as a carbon material for a lithium ion secondary battery, in view of the cost and the durability. However, since the Raman value of an amorphous carbon material is large, there have been problems in that the reversible capacity is small in the range of a practically applicable material and a high capacity cannot be obtained due to the difficulty in increasing the density of an active material layer. On the other hand, a graphite material can achieve a capacity close to 372 mAh/g, which is the theoretical capacity of lithium absorption, and is preferable as an active material. However, when the density of an active material layer including a negative electrode material is increased for increasing the capacity, there have been problems of the increase in the charging/discharging irreversible capacity, the decrease in the large-current charge/discharge characteristics and the decrease in the cycle performance, due to the breakage and the deformation of the material.
In order to solve the above problems, for example, Patent Document 1 discloses that: a nonaqueous solvent secondary battery excellent in the filling property of the carbon material, in the capacity and in the large-current charge/discharge characteristics is obtained; by using spheroidized graphite obtained by a mechanical energy treatment of scale-like graphite carbon particles; and by using a carbon material having a multilayer structure, which is obtained by mixing the obtained spheroidized graphite and an organic compound and then carbonizing the organic compound.
Patent Document 2 discloses that: it is possible to obtain a nonaqueous solvent secondary battery, in which the discharging capacity is high, the charging/discharging irreversible capacity in the initial cycle is kept low and the safety to an electrolytic solution is high; by using a carbon material having a multilayer structure, in which a carbide of an organic substance is adhered to the surface of a graphite carbonaceous substance, and in which the amount of the carbide of the organic substance is adjusted to 12 parts by weight or less and 0.1 parts by weight or more as the remaining carbon amount relative to 100 parts by weight of the graphite carbonaceous substance.
Further, Patent Document 3 discloses that: a nonaqueous solvent secondary battery having a low charging/discharging irreversible capacity in the initial cycle and excellent large-current charge/discharge characteristics is obtained; by using a carbon material having a multilayer structure, in which a carbide derived from a nitrogen-containing resin compound is adhered to the surface of graphite particles in which flat particles are gathered or bound in a state in that the oriented faces are not parallel to each other; and by introducing a certain amount of nitrogen atom on the surface of the carbon material having a multilayer structure.
On the other hand, Patent Document 4 discloses that: a nonaqueous solvent secondary battery having a low charging/discharging irreversible capacity in the initial cycle and excellent high-temperature preservation property is obtained; by letting spheroidized graphite obtained by a mechanical energy treatment of scale-like graphite carbon particles go through a contact treatment with at least sulfuric acid and hydrochloric acid; and by introducing a functional group including an element selected from sulfur and chlorine to the surface of the carbonaceous particles.